1. Field of the Invention
The invention relates to centrifugal pumps. More particularly, the invention relates to a centrifugal pump having ceramic bearings, ceramic thrust washers, and a water cooling channel.
2. State of the Art
Centrifugal pumps utilize an impeller housed in a volute. Fluid enters the volute either axially, radially, or tangentially relative to the impeller and exits either axially, radially, or tangentially depending on the direction of impeller rotation. Centrifugal pumps may be driven by an AC motor or a DC motor. In either case, the pump impeller may be magnetically coupled to the rotor of the motor so that the workings of the motor can be hermetically sealed and isolated from the fluids passing through the pump.
Prior art FIG. 1 illustrate a typical AC motor driven volute pump 10. The pump 10 includes an AC motor 12, a pump volute 14 and an impeller shaft 16 which is coupled to an impeller 18 having a plurality of radial vanes or fins 20. The pump volute 14 is symmetrical about a vertical axis with an axial inlet port 22 and a radial outlet port 24. The impeller 18 is arranged axially with the inlet port 22. Fluid entering the inlet port 22 is free to flow around the impeller 18 and into the spaces between the vanes 20. Regardless of the direction of rotation of the impeller hub 18 and vanes 20, the vanes will create a centripetal force resulting in a low pressure condition at the impeller 18. This low pressure condition will draw fluid into the volute 14 via the inlet port 22. The fluid will enter the spaces between the vanes 20 whereupon it will be driven radially outward from the volute 14 in either a clockwise or counterclockwise flow.
In a magnetic drive type centrifugal pump, the impeller shaft 16 has permanent magnets embedded in it which are acted upon by alternating magnetic fields inside the motor 12 to cause the shaft to rotate. The shaft 16 must be rotatably supported by two bearing surfaces 16a, 16b at opposite ends of the shaft. These bearing surfaces must be very low friction and must also be resistant to abrasion caused by gritty substances contained in the fluid being pumped. The exact design and construction of such bearing surfaces have been the subject of much research and many complicated and expensive designs have been proposed. In particular, ceramic bearing surfaces have been proposed for radial and thrust surfaces. Ceramics are difficult to mold or machine into complex shapes and need to be kept cool especially if they are mounted in a material having a relatively low melting point such as a thermoplastic. These issues are further complicated by the need for both radial and thrust bearings in centrifugal pumps.